p. 1

Topic 2: Basics of Power and Energy

• Power vs. Energy

• Important Power Values (k = kilo, M = mega, G = giga, T = tera)

– "Caveman" ~ 100 W, U.S. per capita ~ 10 kW,

– Windmill ~ 1 MW, Nuclear power plant ~ 1 GW

– Total U.S. ~ 3 TW, Total world ~ 15 TW

• U.S. energy consumption

– Sectors: industrial, transportation, residential, commercial

– Sources: oil, coal, natural gas, nuclear, hydroelectric, etc.

• Types of Energy

– Kinetic, Gravitational Potential, Thermal, Electrical

p. 2

Power vs. Energy

POWER = RATE of energy consumption = energy per unit time

Units of watts (1 W = 1 Joule/sec) or kilowatts (1 kW = 1 kJ / sec)

What is the U.S. per capita power consumption? (a) 100 W (one 100 W bulb ALWAYS on)

(b) 10 kW (ten 1 kW hair dryers ALWAYS on)

ENERGY = power × time

Units of kilowatt-hours (kWh) or kilojoules (kJ)

1 kWh = 3,600 kJ (see notes section on PPT slide for calculation)

p. 3

Caveman(2,000 kcal/day)

=Power = Energy per unit time = Watts (Joule/sec)

POWER = 100 Watts

ONE Light Bulb

About how much does it cost to run a 100 W light bulb for one year? (a) $1 (b) $10 (c) $100(see notes section on PPT slide for calculation)

p. 4

U.S. "per capita"

=

POWER = 10 Kilowatts (kW)

100 ×

10,000 Watts

or 10 hair dryers!

p. 5

=

ONE Windmill

POWER = 1 Megawatt (MW)

100 ×

1,000,000 Watts

p. 6

ONE Nuclear Power Plant

= 1,000 ×

POWER = 1 Gigawatt (GW)

1,000,000,000 Watts

p. 7

Power Values

Power delivered to the Earth by the Sun equals 100,000 terawatts (TW) or 1017 watts (W).

One terawatt (TW) equals how many watts (W)?(a) 1 million watts (106 W)(b) 1 billion watts (109 W) (c) 1 trillion watts (1012 W)

What is the total power consumption of the world's ~7 billion people?(a) 1 TW (b) 15 TW (c) 100 TW

The per capita power consumption for the world is __________ than the per capita power consumption in the U.S. (a) higher (b) lower

(see notes section on PPT slide for calculation)

p. 8

Power and Energy for Human Heart!

The human heart has a power output of 1 to 5 Watts.

For a woman with a 1-Watt heart, about how many gigajoules (GJ) of energy output does this correspond to over her 100-year lifetime? (Format = X)

Hint: 1 year ~ 3107 s (about 30 million seconds!) 1 W = 1 J/s and 1 GJ = 109 J

Power = 1 - 5 W

p. 9

Power and Energy Cost for Incandescent Bulb

A 100-watt incandescent light bulb costs approximately $100 to run for one year. Using the same pricing ($1 per watt for 1 yr usage), what is the "cost" for the energy produced in one year by a 1-GW nuclear reactor?

(a) $100 million

(b) $1 billion

(c) $10 billion

The unit of "watt×yr" (or 1 watt for 1 year) is a unit of:

(a) Power (b) Energy

p. 10

U.S. Energy Consumption

Transportation29%

22%Residential

19%Commercial

30%Industrial

AB

Rank from largest to smallest the three major sectors. (3-digits)

BUILDINGS

C

p. 11

U.S. Energy Sources

What percent of U.S. energy comes from fossil fuels? (2-digit answer)

Rank the following sources for total U.S. energy from largest to smallest. (4-digit answer) (a) Hydroelectic

(b) Coal or Natural Gas (c) Oil (d) Nuclear

Oil

37%

Natural Gas25%

Coal20%

Nuclear9%

Biomass 4%

Hydro3%

Wind0.7%

Other0.5%

p. 12

World Energy Consumption per Capita

http://commons.wikimedia.org/wiki/Image:Energy-consumption-per-capita-2003.png

What countries have very high (red!) per capita energy consumption? (Enter ALL in NUMERIC order)

(1) U.S. (2) Australia (3) Japan (4) Russia (5) Saudi Arabia

p. 13

Types of Energy

Kinetic (KE) = energy of motion of objects

Potential (PE) = energy of position

Thermal = energy of motion of atoms or molecules

Electrical = energy of current flowing in a circuit

Chemical = energy of atomic and molecular bonds

Nuclear = energy from breaking or joining nuclei

p. 14

Potential & Kinetic Energy

As a rock falls, its potential energy PE is converted into kinetic energy KE.

Due to energy conservation,the rock’s total PE at the top equalsits KE just BEFORE hitting the ground.

What type of energy does the rock have AFTER it hits the ground? (a) kinetic (b) potential (c) neither (converted to thermal energy)

Figure from Giancoli

All PE

All KEBEFORE hitting

Half PE Half KE

(assume PE = 0 at ground height)

p. 15

Motion on a U-track

Which energy is maximum at the bottom? (a) kinetic (b) potential

p. 16

Potential Energy

Gravitational potential energy PE is the energy associated with the height of an object from the ground.

PE equals the object’s mass m times its height h times its gravitational acceleration g (= 10 m/s2).

PE hmg If the height of a ball is tripled, then how many times larger is its

potential energy?

p. 17

Simple Generator (Phet animation)

What is the order of the types of energy starting from the falling water and ending with the lightbulb? (4-digit answer)

(a) electrical energy

(b) potential energy (gravitational)

(c) light energy

(d) kinetic energy

p. 18

Hydropower uses the gravitational potential energy from “falling” water.

Higher “head” (height difference) and flow rate give higher power.

If the height of the dam is doubled, then the energy output is how many times larger? (a) 1.5 times (b) 2 times (c) 4 times

Hydroelectric Dam

Initial Height

Final Height

p. 19

Kinetic Energy

Kinetic energy KE is the energy of motion for an object.

Kinetic energy equals one-half the object’s mass m times its velocity v (or speed) SQUARED.

12

2KE mv

If the speed of a car is doubled, then its kinetic energy is four times larger (equals 2 x 2).

If the speed of a car is tripled, then how many times larger is its kinetic energy?

A car at 70 mph has TWICE the kinetic energy than at 50 mph!

p. 20

Speed: Metric and English Units

“Quick” conversion from m/s to mph: double and THEN add 10%

If a car travels at 30 m/s, then how fast is that in mph?Do it in your head!

If a sprinter runs at 10 m/s, then what is her speed in mph?

1 mile 3600 s ×

10×

1609 m 1

m22 miles/

hrshr

p. 21

Kinetic Energy of Car

If a 1000-kg car travels at 66 mph (or 30 m/s), then find its kinetic energy in kilojoules (kJ).

12

2 UNITS: in kg, in m/s, in Jm v m v KEKE

p. 22

Electrical EnergyToday, end-use electrical energy consumption is 13% of total U.S. energy consumption. But

more energy is needed to generate electricity because of inefficiencies.

It takes about 3 kW of input power to generate 1 kW of electrical power. Approximately what percentage of total U.S. energy is then used to GENERATE end-use electrical energy?

(a) 20% (b) 30% (c) 40%%

ele

ctric

al e

nerg

y

1950 2000

13%

3%

END-USE Electrical Energy

Consumption

p. 23

Biomass-Wood 0.9% Biomass-Waste 1.8%

Wind 1.8% Solar PV 0.02%

U.S. Energy Sources for Electricity

Natural Gas

23%

45%

Coal

1%Oil

Rank the following sources for U.S. electrical energy from largest to smallest. (4-digit answer) (a) Hydroelectric

(b) Nuclear or Natural Gas (c) Oil (d) Coal

Nuclear20%

7%

HydroOther 0.4%

Geothermal 0.4%

p. 24

History of ElectricityAncient societies knew of electric charge – electric eels, rubbing amber

caused materials to “stick” (Greek word for amber = elektron)

What attractive force acts between materials rubbed with amber? (a) gravitational (b) electrostatic (c) strong nuclear

William Gilbert (1544-1603)coined term “electricity”

p. 25

History of Electricity

Benjamin Franklin (1752): experiments with electricity/lightning

Luigi Galvani – made legs of dead frogs move with dissimilar electrodes

Alessandro Volta (1791-1800) - built a “voltaic” pile (early battery)

Franklin thought that positive charge flowed in wires. Was he right? (a) yes (b) no

Voltaic Pile

Disney's Ben Franklin Video

p. 26

Electric Charge

What are the positively charged particles in matter?

What are the negatively charge particles in matter?

What particles “flow” in wires to create electric current?

(3-digit answer)

(1) electrons (2) neutrons (3) protons (4) positrons

p. 27

Static Electricity (Phet animation)

If two DIFFERENT materials touch each other, then electrons move from one material to the other because one material “gives up” electrons easier.

If electrons move between objects, then the objects become oppositely charged and _________ each other.

(a) repel (b) attract.

Positive Hair

– –– –

+ + ++

Electrons move from hair to balloon

Negative Balloon

p. 28

Static Electricity (Phet animation)

When Travolta rubs his foot on the carpet, ______ are transferred between the carpet and his body.

When Travolta then touches the door knob, _______ move between his charged body and the grounded door. It can hurt!

(1) electrons (2) protons (2-digit answer)

p. 29

Light Bulb Circuit (Phet animation)

Electrical current = motion of electrons (units of Amperes or A)

Electrical voltage = difference in charge causing current (Volts or V)

In the light bulb circuit, how do the electrons move in the wires?

(a) from (+) to (–) OR (b) from (–) to (+) battery terminal

What is the voltage of a D-cell battery? (a) 1.5 V (b) 6 V

battery

wire

light bulb

p. 30

Resistor Circuit (Phet animation)

When the battery voltage is increased, the current ________ .

When the circuit resistance is increased, the current ________ .

(1) increases (2) decreases (2-digit answer)

p. 31

Electric Oven to Cook a Turkey

If a 5,000 watt electric oven is on for 10 hours to cook a turkey, how many kilowatt-hours (kW-hrs) of energy is used?

If the power company charges 10¢ per kWh, then how much did it cost in dollars to cook your turkey?